This invention is directed to a novel compound analogous to somatostatin, which is known as the peptidal release inhibiting factor and exhibits unusual biological activity in human beings and warm blooded animals. More particularly, it is directed to the undecapeptide represented by the following formula: ##STR2##
Following the first isolation of somatostatin by Krulich in 1973, somatostatin has been demonstrated to inhibit the secretion of not only growth hormones but also insulin and glucagon, and in conjunction with the findings that an excess of glucagon plays in important role in causing diabetes and that growth hormones take part in the development of diabetic syndromes, efforts have been made to develop somatostatin derivatives which may strongly and specifically inhibit the secretion of glucagon and growth hormones.
The present invention has been made in furtherance of the above efforts and now provides the novel peptide of formula (I), tentatively designated by the inventors as Des-(Ala.sup.1,Gly.sup.2)-(D-Trp.sup.8,D-Asu.sup.3,14)-somatostatin, which exhibits unusual biological activities.
Independent of the inventors' investigation, a new synthetic peptide, the so-called DL-Asu-type somatostatin, was reported in the Journal of the American Chemical Society, Volume 98, page 2367, Apr. 14, 1976, in which its inhibiting activity for the release of growth hormones was disclosed to be only half that of somatostatin of natural origin. This very low activity was assumed by the inventors to be due to employment of optically inactive DL-.alpha.-aminosuberic acid as a starting material.